The present invention relates to an optical image sensor used in a facsimile or a copying machine and optically sensing an image, such as, for example, characters, numerals and a figure, on a document.
In an equipment, such as a facsimile or a copying machine, the image on a document is sensed by optical image sensing means, located in a body case, by utilizing the reflection of light emitted from a lamp located in the body case toward the image on the document through an elongated image sensing window formed on the body case while the document is moved at a predetermined speed on the image sensing window.
The lamp is a linear type fluorescent lamp. The fluorescent lamp is disposed in the body case so as to be parallel to the image sensing window at a position separated from the image sensing window at a predetermined distance. The standardized fluorescent lamp, which can ensure sufficient illuminance on the document in the image sensing window to prevent the optical image sensing means from erroneously sensing, is longer than the length of the image sensing window. In the optical image sensor of the conventional equipment described above, the linear type fluorescent lamp is disposed in the body case so as to bring the center in the longitudinal direction thereof into coincidence with that of the image sensing window, so that the both ends of the fluorescent lamp are projected from the both ends of the image sensing window at substantially equal distance. Thus, the optical image sensor of the conventional equipment described above has spaces for containing the both ends of the fluorescent lamp at the outside of the both ends of the image sensing window. Each of the pair of spaces has not small volume which can merely contain each of the both ends of the fluorescent lamp but has relatively large volume as compared with the volume of each of the both ends of the fluorescent lamp so as not to form projections on the outer surface of the case body. Main components of the optical image sensor of the equipment described above are disposed on a chassis in a space lying between the both ends of the image sensing window. The volume of each of the pair of spaces for containing the both ends of the fluorescent lamp is relatively larger than the volume of each of the both ends of the fluorescent lamp as described above but is too small to contain relatively large components in the equipment described above. Therefore, the pair of spaces for containing the both ends of the fluorescent lamp are not sufficiently utilized, and the spaces for containing the both ends of the fluorescent lamp have become dead spaces.
such dead spaces can be eliminated by providing a non-standardized and specially sized line type fluorescent lamp. Such lamp which can ensure sufficient illuminance on a document in the image sensing window to prevent the optical image sensing means providing erroneous reading and, nevertheless it has substantially the same length as that of the image sensing window. Utilization of such non-standardized and specially sized linear type fluorescent lamp is problematic because it causes the maintenance of the equipment to be more expensive as compared to when the standardized fluorescent lamp is used, because such non-standardized and specially sized linear type fluorescent lamp is more expensive than the standardized linear type fluorescent lamp and can be obtained only with difficulty.